Source : Webster's Revised Unabridged Dictionary (1913)

Fabulous \Fab"u*lous\ (f[a^]b"[-u]*l[u^]s), a. [L. fabulosus;
   cf. F. fabuleux. See {Fable}.]
   1. Feigned, as a story or fable; related in fable; devised;
      invented; not real; fictitious; as, a fabulous
      description; a fabulous hero.

            The fabulous birth of Minerva.        --Chesterfield.

   2. Passing belief; exceedingly great; as, a fabulous price.
      --Macaulay.

   {Fabulous age}, that period in the history of a nation of
      which the only accounts are myths and unverified legends;
      as, the fabulous age of Greece and Rome. --
      {Fab"u*lous*ly}, adv. -- {Fab"u*lous*ness}, n.

Source : WordNet®

fabulous
     adj 1: extremely pleasing; "a fabulous vacation" [syn: {fab}]
     2: based on or told of in traditional stories; lacking factual
        basis or historical validity; "mythical centaurs"; "the
        fabulous unicorn" [syn: {mythic}, {mythical}, {mythologic},
         {mythological}]
     3: barely credible; "the fabulous endurance of a marathon
        runner"